MORPHOLOGY OF THE ABDOMINAL-WALL IN THE BAT, PTERONOTUS-PARNELLII (MICROCHIROPTERA, MORMOOPIDAE) - IMPLICATIONS FOR BIOSONAR VOCALIZATION

We investigated the structure of the abdominal wall of Pteronotus parn ellii and made comparisons with eight other species of Microchiroptera and one megachiropteran. Similar to other mammals, the abdominal wall of bats consists of the three flank muscles laterally and the m. rect us abdominis ventrally. In Microchiroptera, flank muscles are mostly c onfined to dorsal portions of the wall. The mm. transversus abdominis and obliquus internus abdominis form the bulk of the wall; the m. obli quus externus is poorly developed. Ventrolaterally, a large portion of the wall is a dense, bilaminar aponeurosis, composed of collagen, ela stin, and fibroblasts. The thicker, superficial lamina derives from th e mm. obliquus internus and transversus abdominis. The deep lamina is a continuation of the transversalis fascia. Collagen fibers of the two fused laminae are oriented orthogonally, resulting in a resilient, co mposite fabric. Fascicles of the flank muscles are oriented along the margins of the aponeurosis so that their forces appear to be concentra ted onto the aponeurosis. We suggest that this system is adapted for t he regulation and generation of intra-abdominal pressure. The abdomina l wall of Pteropus, the one megachiropteran examined, lacks the derive d aponeurosis and is similar to other mammals. We consider the abdomin al wall of Microchiroptera to be analogous to the diaphragma, in that it functions in the regulation of pressure within body cavities and fa cilitates biosonar vocalization. (C) 1995 Wiley-Liss, Inc.